Since the appearance of nuclear power plants, various technologies have continuously developed and become one of the indispensable energy of the major countries in the world. The key equipment of nuclear power plant is the reactor, which has developed several types, including pressurized water reactors, boiling water reactors and gas-cooled reactors. Spent fuel produced by the reactor operation has two main features, that is, of having radioactivity and continuously release residual heat, so it is required to set up special facilities for spent fuel storage.
Through several decades of development, a complete nuclear power system has formed in China, several types of nuclear power plants have been developed and introduced, including pressurized water reactor, heavy water reactor and so forth, where the storage method of spent fuel is mainly pool storage. While developing water reactor nuclear power plants, the technology of utilizing high temperature gas-cooled reactor for power generation has also been developed continuously in China. At present, a demonstration project of high temperature gas-cooled reactor nuclear power plant supported by National Science and Technology Major Project is carrying out, and the design of the project has been completed basically. Different from the pressurized water reactor nuclear power plant, the spent fuel storage technology of the demonstration project fully utilizes the air cooled dry silo storage method for the spent fuel storage canister, which can solve the hazard of loss of coolant accident of the spent fuel pool storage method, and improves the overall safety of high temperature reactor nuclear power plant.
The pebble bed modular high temperature gas-cooled reactor nuclear power plant developed in China has main features of the fourth generation nuclear power plants, which comprise inherent safety, preventing nuclear proliferation, producing high temperature process heat and so on. The pebble bed high temperature gas-cooled reactor utilizes spherical fuel elements with graphite matrix, and the outer diameter of the element is 60 mm. After the spent fuel elements are discharged from the reactor core in high temperature reactor, the spent fuel elements can be loaded into special spent fuel storage canisters, and all of the storage canisters are stored in the spent fuel dry storage facilities.
In summary, at present, the pool storage method still is the main storage method for spent fuel in nuclear power plants. The main reason is that the pool storage method can solve the issue of radiation shielding and residual heat removal conveniently, that is, water has the function of radiation shielding and can serve as a carrier for residual heat to cool spent fuel. However, the pool storage also has several shortcomings, which lie in that when loss of coolant accident occurs in the pool, if the spent fuel is exposed out of the water level, not only water cannot play the role of radiation shielding, but this situation may also deteriorate residual heat removal conditions of spent fuel, which even results in burnout of spent fuel and release of radioactive materials.
The spent fuel dry storage technology developed recently can solve the issue mentioned above effectively, which is mainly used for the spent fuel that has already been stored in a pool for a while. After that cooling time, the residual heat level of the spent fuel is low, and the radiation dose is reduced also. The spent fuel dry storage technology don't need water sources, so the radiation shielding of the spent fuel mainly depends on storage facilities, and the residual heat removal mainly depends on air cooling.